Flame-retardant rayon containing halogenated phosphonitrilate polymer



United States Patent Ofifice 3,505,087 Patented Apr. 7, 1970 US. Cl.106-15 9 Claims ABSTRACT OF THE DISCLOSURE Flame-retardant regeneratedcellulose filaments and filamentary articles containing dispersedtherein a flameretardant amount of a substantially water-insoluble,liquid, halogenated phosphonitrilate polymer, and a method of preparingthe filamentary articles are disclosed herein.

This in a continuation-in-part application of eopending patentapplication Ser. No. 566,757, filed July 21, 1966, now Patent No.3,455,713.

It is desirable for many textile purposes to provide cellulose fibersand yarns having greatly decreased flammability. The production of rayonwhich demonstrates acceptable flame-retardant properties for all textilerequirements, using inexpensive and commercially suitable chemicalflame-retardants, has not been satisfactorily accomplished to date.

The application of various organic and inorganic flameretardants to thesurface of cellulose fibers and fabrics has not produced the desiredresult for a number of reasons. In many instances, the chemicalflame-retardant is effectively removed when the fabric is washed withwater or dry cleaned with solvents. Other flame-retardant chemicalswhich may be applied to the fabric surface and retained after washingare generally too costly. In other cases, the chemicals used may providesome lasting reduction in flammability but destroy fiber and fabriccharacteristics, such as tenacity, softness, whiteness, and dyeability,which are desirable and necessary for textile applications.

In the manufacture of rayon by the viscose method, it has been proposedto add various flame-retardant chemicals to the viscose prior tospinning. This approach presents many additional problems because of theparticular chemistry of the viscose process. Accordingly, theflameretardant must be stable and inert with respect to the highlyalkaline viscose and also with respect to the acid regenerating bathinto which the viscose is extruded. It must not be extracted duringspinning and processing. Furthermore, the added material must notinterfere with the spinning process, i.e., cause clogging of thespinnerets. The rayon produced from the flame-retardant containingviscose must not be degraded in any of its properties and must have asubstantially reduced flammability.

It is not an object of this invention to provide a flameretardant rayonfiber without appreciable degradation of any fiber properties.

It is a further object of this invention to provide a process forpreparing a flame-retardant rayon fiber which retains substantially allof the properties of ordinary rayon.

These and other objects are achieved in accordance with this inventionwhich comprises a regenerated cellulose filament having dispersedtherein a substantially water-insoluble, liquid phosphonitrilate polymerhaving the following general formula:

wherein R and R are the same or different alkyl, alkenyl, arylalkyl oraryl radicals wherein the alkyl and alkenyl radicals have from one tosix carbon atoms and the aryl groups have 6 to 10 carbon atoms and, atleast one of the OR or OR' groups of the polymer has one or more halogenatoms attached to the carbon atoms of R or R, and n is an integer of atleast 3. For example, R and R include halogen substituted andunsubstituted ethyl, propyl, isopropyl, butyl, isobutyl, arnyl, isoamyl,hexyl, allyl, crotyl, phenyl, naphthyl and cresyl radicals. Where R ismethyl R must be a radical of a greater number of carbon atoms since themethyl radical is not readily halogenated and also tends to make thepolymer more Water-soluble. In the preferred embodiment of thisinvention, R and R are both halogenated ethyl or propyl radicals sincecompounds where R and R are the same are more easily prepared, andphosphonitrilate polymers having fewer carbon atoms tend to be morewater-soluble, whereas the presence of more carbon atoms providesproducts having a lower percentage of phosphorus thereby reducing theireffectiveness. However, mixed esters wherein R and R are differentradicals depending on the combination of substituent groups andhalogens, may provide superior results. Furthermore, the halogen atomsincluded herein are chlorine, bromine and fluorine. Iodine is excludedsince derivatives thereof are unstable.

The liquid phosphonitrilate polymer is a cyclic trimer, tetramer orhigher cyclic polymer, or a linear polymer and is preferably employed asa mixture of these isomers for economic reasons. It has been found,however, that the pure polymeric isomer is effective for the purposes ofthis invention.

The amount of phosphonitrilate flame-retardant dis persed in theregenerated cellulose filament varies from about 5 to about 30% andpreferably from 10 to 25%, based on the weight of the filament.

The method of this invention comprises incorporating the above describedliquid phosphonitrilate in a viscose solution and spinning the viscosein the shape of one or more filaments into a coagulating andregenerating medium. The formed filaments are aftertreated usingtechniques well-known in the rayon field to provide continuousfilaments, fibers and yarn, as well as staple fibers. These may then beused to prepare any known textile article in which the flame-retardantproperty is desirable.

The flame-retardant phosphonitrilate of this invention is a liquid ofpumpable consistency which is preferably used as a crude reactionproduct, prepared, for example, in a known manner by the conversion ofthe corresponding polymeric phosphonitrilic chlorides to the specifiedesters, and then halogenated. Refined products such as the trimer arealso quite useful. Halogenation, for example, may be carried out asshown by Hamalainen et al., Textile Research Journal, February 1956, pp.14l 144, and U8. Patent 2,825,718. The esters or mixed esters may alsobe chlorinated or fluorinated similarly.

The halogenated esters are also former, for example, by reacting theliquid polymers of phosphonitrilic chloride with a compound which willform a halogenated ester of the phosphonitrilic chloride, for example,ethylene chlorohydrin and ethylene bromohydrin, or halogenated alkylalcohols, for example, as shown in US. 2,681,295.

The product formed by these reactions is an oily liquid and may beincorporated in viscose as such or in suitable solutions or aqueousemulsions. Preferably a controlled amount of the flame-retardanthalogenated phosphonitrilate is injected into the viscose just prior toits extrusion through the filament forming spinnerets. The viscose isthen spun into an acid bath and processed in a conventional manner.

The following examples are set forth to demonstrate this invention.

EXAMPLE 1 295.5 grams (3.67 moles) of ethylene chlorohydrin was addeddropwise over a 75 minute period to a stirred solution of 133.4 grams(2.3 mole equiv.) of the cyclic trimer of phosphonitrilic chloride in1000 ml. of pyridine. Initially the reaction mixture was at 20 C., butthe temperature rose rapidly reaching 38 C. after about 70 grams ofethylene chlorohydrin had been added. External cooling reduced thetemperature to about C. where it was held for the remainder of theaddition. The reaction mixture was then stirred at room temperature for24 hours.

After the 24 hours of stirring, some excess of pyridine was distilledoff under vacuum (150 minutes, 40-41 C.) and the residue poured onto icewater (1000 ml.). The product was extracted with chloroform (300 ml.)and the chloroform solution separated, washed twice with dilutehydrochloric acid (100 ml. per wash) and then twice with water (300 ml.per wash). The aqueous layers were extracted successively withchloroform (300 ml.) and the chloroform solutions combined, dried andfiltered.

Evaporation of the chloroform on a rotary evaporator left an oilyresidue which was stirred under vacuum for 5.5 hours (40 C., 0.02 mm.).The final product was a straw colored oil (225.5 grams, 95%) with afaint mistiness which was not removed by filtering.

A nuclear magnetic resonance spectrum of this material showed a triplet3.75 p.p.m. and a complicated, poorly resolved pattern at 1:1 ratio.This result was consistent with the formula for2,2,4,4,6,6-hexa(2-chloroethoxy) cyclotriphosphazatriene or2-chloroethyl hexaester of trimeric phosphonitrilic chloride, and therewere no significant impurities. Analysis of the compound showed 22.8%carbon, 3.95% hydrogen, 34.7% chlorine, 7.54% nitrogen and 16.9%phosphorus. Theoretical requirements for the compound are 23.6% carbon,3.95% hydrogen, 34.8% chlorine, 6.9% nitrogen and 15.2% phosphorus.

A compound prepared in this manner was injected into the viscose linesupplying the spinnerets for manufacturing rayon in a metered amountbased on the weight of the cellulose in the viscose. This viscose wasspun into a conventional aqueous acid spin bath comprising 9.0% sulfuricacid, 2.0% zinc sulfate and sodium sulfate at 55 C. The resulting yarnwas processed by passing it through a series of baths including waterwash, desulfurization, bleaching, bleach acid, anti-chlorine, and softfinish baths. The yarn was dried and collected.

A yarn flammability test was conducted with yarn produced as describedabove. The test consisted of first preparing a yarn bundle by wrappingthe yarn around the closed fingers of an extended hand to produce abundle of 6000 denier and then removing it from the hand. The yarnbundle is twisted five times and then doubled on itself to produce anintegrated yarn bundle, one and one-half inches long and of 12,000denier size. The free ends of the yarn bundle are clamped in forceps,and the bundle, held in horizontal position, is passed through the tipof the flame of a Fisher burner in an oscillating motion at a rate ofone pass per second. The burner flame is adjusted to a two inch heightand a blue flame. The number of passes to induce flaming of the sampleis determined. A control yarn bundle (yarn con- .tains noflame-retardant inflames in 1 or 2 passes and flame-retardant yarns areclassified for inflammability as follows:

1-2 passes-poor 3-4 passes-fair 56 passes-good 7-9 passes-very good toexcellent 10 or more passes-excellent Rayon yarn containing about 15 wt.percent of the 2-chloroethyl hexaester of trimeric phosphonitrilicchloride was rated excellent in the above test procedure with noevidence of after-glow. After-glow represents combustion without avisible flame.

Retention of the amount of flame-retardant in the yarn after the above.described complete processing of the spun yarn based on phosphorusanalysis showed 91.0%. The yarns esthetic properties were substantiallythe same as ordinary rayon.

EXAMPLE II A similar procedure for preparing the chlorinated ester ofthe cyclic trimer of phosphonitrilic chloride as shown in Example I wascarried out except that a mixture of phosphonitrilic chloride polymersobtained as the crude product from the preparation of the liquidphosphonitrilic chloride polymer was employed in place of the purecyclic trimer. The mixture contained mostly trimer and tetramers withsome higher cyclic and linear polymers of phosphonitrilic chloride. Theyield was 85.4% and analysis of the product showed 23.3% carbon, 4.05%hydrogen, 34.9% chlorine, 16.0% phosphorus and 7.4% nitrogen.

The product of the above reaction was similarly injected into viscoseand the viscose spun and processed as described in Example I. The yarn,containing about 15% by weight of the injected product, was subjected tothe flame test and showed very good flame retarding with no after-glow.After exposure to ultraviolet light in a Fadeometer for 50 hours, theloss of yarn strength was not greater than conventional rayon.

EXAMPLE III The 2,3-dichloropropyl hexaester of the cyclic trimer ofphosphonitrilic chloride was prepared by chlorination of the hexaallylester of phosphonitrilic chloride. This was injected into viscose andthe viscose spun and processed. The yarn, containing 25% by weight ofthe chlorinated phosphonitrilate was flame-retardant.

Other water-insoluble, liquid halogenated polyphosphonitrilic esters,e.g. chlorinated, brominated and fluorinated allyl esters ofpolyphosphonitrilic chloride; adducts of bromoform and allyl ester ofpolyphosphonitrilic chloride; 2,3-dibromopropyl ester ofpolyphosphonitrilic chloride; 1,3-dichloropropyl ester ofpolyphosphonitrilic chloride; chlorophenyl ester of polyphosphonitrilicchloride; bromonaphthyl ester of polyphosphonitrilic chloride;halogenated or partially halogenated mixed esters, e.g. bromopropyl,ethyl ester of polyphosphonitrilic chloride; fluoropropyl, methyl esterof polyphosphonitrilic chloride; chlorophenyl, methyl ester ofpolyphosphonitrilic chloride; etc., can be injected into viscose toprepare rayon as shown in the foregoing examples.

As set forth in the statement of the invention, it is not necessary thatthe OR and OR groups attached to each phosphorus atom in the polymericchain be halogenated. That is, for example, the hexaester of the cyclictrimer of phosphonitrilic chloride has six substituent groups. Inaccordance with this invention, from one to six of these groups can behalogenated.

Some of the halogenated esters will be more permanently retained in theyarn than others, some require addition in greater amounts to theviscose to obtain the desired flame-retardancy but the greatestadvantage of the flameretardant of this invention is that it can beinjected into viscose and spun into a yarn which retains its normalsoftness and hand. This is because the halogenated ester is a viscousliquid held within the regenerated cellulose matrix. Phosphonitrilicesters which are solids tend to produce harsh yarn and are difiicult tospin in viscose.

Those halogenated esters which are not permanently retained by fabricmade of the rayon yarn after continued washing will be useful for rayonintended for use in disposable garments.

I claim:

1. Regenerated cellulose filaments and filamentary articles, saidfilaments having dispersed therein a flame-retardant amount of asubstantially water-insoluble, liquid phosphonitrilate polymer havingthe following general formula:

wherein R and R are the same or different alkyl, alkenyl, arylalkyl oraryl radicals wherein the alkyl and alkenyl redicals have from 1 to 6carbon atoms and the aryl radicals have from 6 to 10 carbon atoms and,at least one of the -OR or -OR groups of the polymer ha one or morehalogen atoms attached to the carbon atoms of R or R, and n is aninteger of at least 3.

2. The regenerated cellulose filaments of claim 1 containing from about5 to about 30% based on the Weight of the cellulose, of the liquidphosphonitrilate polymer.

3. The regenerated cellulose filaments of claim 1 wherein R and R areboth 2-chloroethyl radicals.

4. The regenerated cellulose filaments of claim 1 wherein R and R areboth 2,3-dichloropropyl radicals.

5. The regenerated cellulose filaments of claim 1 wherein R and R aredifferent radicals and one of said radicals is halogenated.

6. A method of preparing a flame-retardant regenerated cellulosefilament which comprises mixing viscose and a fllame-retardant amount ofa substantially water-inlNi wherein R and R are the same or diflerentalkyl, alkenyl, arylalkyl or aryl radicals wherein the alkyl and alkenylradicals have from 1 to 6 carbon atoms and the aryl radicals have from 6to 10 carbon atoms and at least one of the -OR or OR' groups of thepolymer has one or more halogen atoms attached to the carbon atoms of Ror R, and n is an integer of at least 3; shaping the mixture into afilament, and coagulating and regenerating said filament.

7. The method of claim 6 wherein the viscose is passed under pressure toa spinneret and extruded, and the liquid phosphonitrilate polymer isinjected at a controlled rate into the viscose prior to extrusion. H

8. The method of claim 6 wherein about 5 to about 30% 0f the liquidphosphonitrilate is mixed with the viscose, based on the weight of thecellulose in the viscose.

9. The method of claim 6 wherein R and R are the same and each containat least 2 carbon atoms.

References Cited UNITED STATES PATENTS 8/ 1966 Schappel et al. 7/1969Godfrey.

US. Cl. X.R.

